A team of investigators from the University of British Columbia, University of Zagreb School of Kinesiology, Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia including Dr. David MacLeod of the Department of Anesthesiology, Duke University Medical Center, have published an investigation in elite breath-hold divers of brain oxygenation (http://www.ncbi.nlm.nih.gov/pubmed/25370857). They observed that at maximum apnea (mean 316, range 212-435 seconds), arterial blood gases were (mean values): PO2 29.5 mmHg, PCO2 51 mmHg, arterial Hb-O2 saturation 57%. Despite profound hypoxemia, oxygen delivery to the brain was maintained by augmented cerebral blood flow due to a 50% increase in blood pressure. It was noted that the trigger for the “break point” of the breath hold is still a mystery.